Video won't render properly, only audio?
You have once let Blender create the 25% proxy files and then moved your footage or *.blend file to a different location afterwards so that Blender can't find it any more...

You have to look for the original footage - your clips source video files and put them back in place where they originally were. There's a menu entry in the File menu helping you to find lost files. Or just look at one strip in your VSE and see where it points to and if your source footage is still there or if you can put it back there again. There already are some questions with good answers about this here on BSE...